The present invention is classified as a Residential Fueling Facility (RFF) by the National Fire Prevention Association (NFPA), and relates to a method and system of compressing natural gas at a residence to re-fuel natural gas vehicles. More particularly, it relates to such a method and system especially adapted to the economics of the equipment used to increase the pressure (to pressurize or compress) the gas from a residential gas supply line up to the 3500-4000 pounds per square inch (psi) required to re-fuel on-board storage tanks on natural gas vehicles. The present invention relates, specifically, to the use of a flexible bladder, inside a steel vessel, to receive, and temporarily-store, natural gas from a residential gas supply line. In order to increase the pressure of the temporarily-stored gas inside the bladder, a hydraulic fluid is pumped into the annulus between the outer walls of the bladder and the inner walls of the steel vessel. With continued pumping, the pressure of the hydraulic fluid will exceed the gas pressure inside the bladder and the bladder collapses in size which results in the gas inside the reduced-size container (the bladder) being elevated to a higher pressure. The higher-pressured gas can then be transferred to a compressed natural gas (CNG) storage tank on-board the vehicle being refueled. In the absence of an internal flexible bladder to pressurize the gas, a more-expensive mechanical compressor would have to be used, which would increase the cost to the residence-owner and make it more difficult to re-fuel automotive equipment at home.
The conventional manner of pressurizing (compressing) natural gas, at home, is to utilize commercially-available RRF units which utilize conventional mechanical compressors to boost the pressure of the gas up to the 3500-4000 psi level required to re-fuel on-board storage tanks in natural gas vehicles, which are so expensive as to make the use of CNG to re-fuel vehicles non-competitive with fuels such as gasoline and diesel to re-fuel automotive equipment.
The present invention is intended to solve the need for a more-economical method of pressurizing (compressing) natural gas from the low-pressure available at the standard household gas utility line of approximately 1 psi, which must be boosted up to the 3500-4000 psi level utilizing a multi-stage mechanical compressor. The desired economics are possible due to the elimination of the multi-stage compressor and to replace the compressor with a self-contained pressurization chamber composed of a steel cylinder, a flexible bladder inside the steel cylinder, and a hydraulic system (pump, prime-mover, surge tank) to pump a hydraulic fluid in the annulus between the bladder and the steel walls of the cylinder.
The flexible bladder is a one-piece cylinder-liner which, when filled with gas from the gas supply line, will inflate substantially to the interior walls of the steel cylinder, which will be sized to accommodate the volume of gas required to re-fill the on-board storage tanks of two natural gas vehicles in a slow-fill period (usually approximately 5 hours). The bladder is made of rubberized nylon, or if, by choice, some other member of the elastomer family of synthetic rubbers, compatible with natural gas, fresh water/anti-freeze mix, or mineral hydraulic oil, with one domed-end, the other end open and attached (bonded) to the face of a flange attached to the steel cylinder.
The hydraulic fluid is a matter of choice and can be either a water/anti-freeze mix, or a hydraulic mineral oil.
The present invention is particularly designed for more-economical at-home pressurization of natural gas for natural gas vehicles, utilizing a hydraulic pump instead of a mechanical compressor. While primarily designed for home use, the invention can also serve as a more-economical method of re-fueling natural gas vehicles while at work in business and commercial buildings; in commercial buildings to fuel fork-lift trucks; at airports to re-fuel airline baggage and passenger transports; and generally any other method of transportation involving gasoline/diesel fuels.